Methods and apparatus for transmitting data in a radio communication system including signaling allocation of a common channel

ABSTRACT

According to the invention, signalling of the used common channels is carried out implicitly via the data rate. Several combinations of channels (spread codes) are only permitted as an alternative for particular data rates of the individual services. Transmission capacity is saved since it is not necessary to reserve individual bits inside the TFCI parameter uniquely for the allocation of said common channels to different connections. The invention is especially useful in the downlink of the FDD modus of UMTS mobile radio systems.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for transmitting data in aradio communication system, particularly in mobile radio systems with abroadband radio interface, also called UMTS (universal mobiletelecommunication system).

2. Description of the Prior Art

In radio communication systems, data are transmitted via a radiointerface using electromagnetic waves. The radio interface refers to aconnection between a base station and subscriber stations, with thesubscriber stations being either mobile stations or stationary radiostations. In this context, the electromagnetic waves are radiated atcarrier frequencies situated in the frequency band provided for therespective system. For future radio communication systems, for examplethe UMTS mobile radio system or other 3rd generation systems,frequencies in the frequency band of approximately 2000 MHz areprovided, with the bandwidth of a channel being 5 MHz.

By contrast, with systems like GSM (global system for mobilecommunications), a number of services which also can be transmitted inparallel is provided for the UMTS mobile radio system. Patentspecifications EP 98 122 719 and DE 198 55 194 describe options forsignaling the transport formats for the combination of data for a numberof services. The data for a number of services on a connection aretransmitted via a jointly used physical channel in this case.

The use of jointly used physical channels for transmitting data for anumber of services on a connection to a subscriber station presupposesthat a unique mapping specification indicates the allocation of theservices to different segments of the physical channel.

By way of example, a physical channel is defined by a frequency band anda spread code (CDMA code division multiple access) within a frame.

The following terms are customary for describing the mappingspecification:

Transport Format (TF):

A transport format defines a data rate, a coding, scrambling(interleaving), a data rate adjustment by puncturing and an errorprotection specification for a transport channel for a service.

Transport Format Set (TFS):

This denotes a set of possible transport formats which are permitted fora specific service.

Transport Format Combination (TFC):

This term indicates a possible combination of transport formats for thevarious services which are mapped onto a common physical channel.

Transport Format Combination Set (TFCS):

This denotes a set of possible TFCs as a subset of all TFCs which arepermitted for a specific connection.

Transport Format Combination Identifier (TFCI):

This information item indicates the currently used combination oftransport formats within the TFC.

In order to be able to select the currently used combination oftransport formats for the various services in line with requirements,the TFC needs to be able to be changed, and hence the TFCI needs to besignaled regularly. This signaling ties up transmission capacity,however. The greater the number of possible combination options (TFCS),the more capacity is required for signaling.

In the case of the broadband CDMA system chosen for the FDD mode (FDDfrequency division duplex) for the UMTS mobile radio system, whentransmitting from the base station to the subscriber station in thedownlink direction, the problem arises that the number of orthogonalspread codes which are useful is limited, which makes it more difficultto support variable data rates. Thus, with relatively high trafficdensities in the system, it is not possible to allocate to allsubscriber stations as many dedicated (i.e., used exclusively by thesubscriber station) channels (DCH) as they need for transmission attheir respective highest data rate.

For this reason, common channels, “shared channels” (DSCH downlinkshared channel), are defined in the downlink direction, in this regardcf. ETSI, SMG2, UMTS-L1, Tdoc SMG2 UMTS-L1 559/98, dated Nov. 9, 1998.The common channels are formed within the broadband frequency band byspread codes which are temporarily allocated to various connections orsubscriber stations for the duration of one or more frames in each case.In this context, however, the problem arises of how it is possible tosignal to a subscriber station with minimum complexity whetherinformation is being transmitted for the subscriber station and, if so,in which of these common channels.

In addition, ETSI SMG2 UMTS-L1, Tdoc SMG2 UMTS-L1 559/98, dated Nov. 9,1998, discloses that the data rates for the services transmitted usingtime-division multiplex are signaled using the TFCI parameter, which istransmitted during each frame as part of the control information; i.e.,in-band. To ensure rapid allocation of common channels, explicitsignaling is proposed which uses a particular number of these TFCI bitsexclusively for the purpose of indicating a particular spread code (cf.penultimate page).

This solution has the drawback that, as a result of this, for a givennumber of TFCI bits, the number of combination options for transportformats for the services is significantly limited, which has aconsiderable effect on flexibility when transmitting variable datarates.

The present invention is, therefore, directed to a method and a radiocommunication system which, when using common channels for a number ofconnections, increase the flexibility of resource allocation whentransmitting variable data rates.

SUMMARY OF THE INVENTION

Accordingly, the present invention is based on the idea of implicitlysignaling the used common channels using the data rate, and ofpermitting a number of combinations of channels (spread codes) asalternatives only for particular data rates for the individual services.This saves transmission capacity, because there is no need to reserveany individual bits within the TFCI parameter just for allocating thecommon channels to different connections. The data rate is signaledin-band, with this information relating to the data rate not needing tobe contained in full in each frame. Information from the connectioncontext or from preceding frames likewise can be used for determiningthe data rate.

In accordance with one embodiment of the present invention, mapping thesame combination of transport formats for the services onto variouschannels using the TFCI allows a very high degree of flexibility and canbe achieved for minimum signaling complexity.

The relationship between allocated data rate and common channels to beused is agreed in a separate signaling channel, so that the receiver isable to derive the chosen combination of channels, including one or morecommon channels, from the respective value of the TFCI parameter. Thissignaling of the relationship (mapping specification for the TFCI valuesonto stipulated combinations of the transport formats) advantageouslyoccurs upon connection setup between base station and subscriberstation. The data rate for the TFCI in-band signaling is high and usesconsiderable transmission resources. If it is possible to make savingshere by virtue of generally valid agreements at the start of connection,then the number of TFCI bits required can be reduced, or the number ofcombination options can be increased.

The method according to the present invention and its advantageousdevelopments give rise to the following advantages:

-   -   With purely implicit signaling, there is no additional signaling        complexity, wherein the available TFCI bits can be used        exclusively for signaling the combination of data rates for the        individual services with very fine granularity.    -   Implicit signaling permits a high maximum transmission capacity        to be allocated for each connection. The resultant dependencies        of the possible data rates between the connections become less        significant the more connections are involved and common        channels are available.    -   The additionally possible allocation of the same service        combinations to various common channels using a respective        unique TFCI value permits a very high degree of flexibility to        be achieved.    -   The complexity for signaling common channels can be matched very        precisely to the requirements of the connection and need not        involve whole bits.    -   The use of common channels can be limited to particular,        higher-rate service combinations or those with high data rate        dynamics, while low-rate service combinations are transmitted        exclusively using dedicated channels.    -   It is possible to allocate common channels on a        connection-oriented basis and dynamically, depending on the        current number of used channels.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Preferred Embodiments and the Drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of a radio communication system;

FIG. 2 shows a layer model of the transmission protocols;

FIGS. 3, 4 show data for various services mapped onto jointly usedphysical channels;

FIGS. 5, 6 show tables containing allocation options for common channelsfor a number of connections;

FIGS. 7, 8 show ambiguous allocations and, hence, reduction in thelikelihood of blockages; and

FIG. 9 shows data transmission in frames with in-band signaling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The mobile radio system shown in FIG. 1 as an example of a radiocommunication system comprises a multiplicity of mobile switchingcenters MSC (although only one Mobile Switching Center is shown in FIG.1 for illustrative purposes) which are interlinked and set up access toa landline network PSTN. In addition, these mobile switching centers MSCare connected to at least one respective device Radio network managerRNM (which is also known in the art as a Base Station Control, asindicated in FIG. 1), for controlling the transmission resources. Eachof these devices RNM permits, in turn, a connection to at least one basestation BS.

A base station BS can set up a connection to subscriber stations, e.g.mobile stations MS or other mobile and stationary terminals, via a radiointerface. Each base station BS forms at least one radio cell. FIG. 1shows connections for transmitting user information between a basestation BS and mobile stations MS. Within a connection VI, data for, byway of example, three services S (S1, S2, S3) are transmitted within oneor more physical channels Phy CH, and signaling information, e.g. theallocated radio system resources for a connection V1, is transmitted viaa monitoring channel FACH (Forward link Access CHannel) whichaccompanies the connection.

An operation and maintenance center OMC provides monitoring andmaintenance functions for the mobile radio system or for parts thereof.The functional scope of this structure can be transferred to other radiocommunication systems in which the present invention can be used, inparticular for subscriber access networks with wireless subscriberaccess.

In the radio communication system shown in FIG. 1, both the basestations BS and the mobile stations MS are provided with bothtransmission and signaling devices which communicate with one another.The transmission device is used for transmitting data for a combinationof a number of services S via the currently available physical channelsPhy CH. The physical channels Phy CH may be in the form of dedicatedchannels DCH, i.e. used exclusively by one connection, or in the form ofcommon channels DSCH, i.e. used alternately by different connections V1,V2. A distinction, therefore, needs to be drawn between physicalchannels Phy CH jointly used by a number of services S1, S2, S3 on aconnection V1 and common channels DSCH, which are allocated to a numberof connections V1, V2 but is allocated to just one of the connections V1or V2 for use during a period of time. The allocation of a commonchannel DSCH can be changed very rapidly from frame to frame withoutadditional signaling complexity. The use of a common channel DSCH bydifferent connections at successive times permits, in particular, goodcorrespondence to the high data rate and high dynamics of the data rateof some connections V1, V2.

The signaling device determines TFCI values for the selectedcombinations of transport formats TF for the services S1, S2, S3 andperforms in-band signaling of the transport formats TF. In the separatechannel FACH, the mapping specification for TFCI value to combination oftransport formats TF and used channels DCH, DSCH is signaled.

The layer model shown in FIG. 2 shows the protocols of the radiocommunication system divided into three layers.

Layer 1: physical layer for describing all the functions for bittransmission via a physical medium (e.g., coding, modulation,transmission power monitoring, synchronization etc.).

Layer 2: data link layer for describing the mapping of data onto thephysical layer, and monitoring thereof.

Layer 3: network layer for controlling the resources of the radiointerface.

Layer 3 stipulates the TFCS for a connection, while layer 2 selects acombination (of a TFC) which is signaled in-band using a TFCI, as shownlater.

The parameter exchange between layers 1 and 2 supports the functions oftransferring frames with data for layer 2 via the radio interface and ofdisplaying the status of layer 1 to higher layers. The parameterexchange between layers 1 and 3 supports monitoring of the configurationof the transmission in layer 1 and generates system information relatingto layer 1.

In this case, the mapping of the data for various connections S onto acommon physical channel Phy CH and the signaling of the allocation of acommon channel DSCH correspond to the interaction of layers 1 and 2.

FIGS. 3 and 4 show the need for transport formats TF to be signaled forcurrently transmitted services.

FIG. 3 shows, as an illustration of function, a coding and multiplexunit which maps data from a number of data channels DCH (which eachcorrespond to the data for a service S1, S2, S3) onto a coded commontransport channel CCTrCH. In this context, mapping is a specificationgoverning the bit pattern which is to be used for entering the data intoa serial data sequence. A demultiplexer/allocation device distributesthe data for the coded common transport channel CCTrCH over a number ofphysical channels Phy CH. The physical channels Phy CH are, thus,constantly used to transmit data for a number of services S1, S2, S3 ineach case. A physical channel Phy CH is not allocated to one service S1or S2 or S3 alone, but rather is allocated to the coded common transportchannel CCTrCH with all its services S1, S2, S3.

Since the reception end needs to reconstruct this mapping and needs toread the data from the physical channels Phy CH and present them againin separate transport channels DCH for the services, signaling isnecessary. This signaling in the form of TFCI values depicts thecurrently used combination of the transport formats TF for the servicesand, as shown later, the current allocation of a common channel or of anumber of common channels DSCH. It has been agreed at connection setupwhich combinations are permitted for the connection (TFCS).

Two options in the relationship between data rate and servicecombinations can be implemented (cf. also EP 98 122 719):

-   1. Each data rate GR corresponds to precisely one combination of    transport formats TF.-   2. For each data rate GR, a number of combinations of transport    formats TF are possible which can be distinguished using TFCI    values.

FIG. 4 shows the mapping in a slightly modified form, with it becomingclear that the partial information item TFCI need be signaled only whenphysical channels Phy CH are jointly used by a number of services S1,S2, S3. If a service S1 or S2 or S3 uses one physical channel Phy CHexclusively, then signaling of the partial information item TFCI can bedispensed with.

The allocation of a common channel DSCH to a connection V is shown withreference to FIGS. 5 and 6 using an example having two mobile stationsMS and, hence, two connections V1, V2. Let it be assumed that theconnections 1 and 2 each can transmit their data using the data rates of16, 32 and 48 kbps, with three common channels DSCH each having 16 kbpsbeing available for both connections V1, V2. For the two connections V1,V2, the tables shown in FIGS. 5 and 6 each stipulate which of thesecommon channels DSCH can be used to transmit which data rates. Thistable has been stipulated at the start of connection, but also may bechanged concurrently with the connection.

Since the two connections V1, V2 exist in parallel, only particularcombinations of the data rates are permitted, in order to preventsimultaneous use of the common channels DSCH. These are indicated in thetable shown in FIG. 7.

In this example, only 10 of 16 possible combinations are permitted. Allthe combinations in which more than 16 kbps are transmittedsimultaneously for the two connections V1, V2 must be excluded. Ingeneral, the described implicit allocation of common channels DSCHallows the available channels to be split over all the connections V1,V2 with such flexibility that each individual connection V1, V2 is ableto use a much higher transmission capacity than in the case of fixedallocation of the channels as dedicated channels DCH.

In this case, for statistical reasons, the limitation to particularcombinations becomes less significant the more connections V1, V2 andcommon channels DSCH are available. This assumes that the ratio of themaximum data rate required by all connections V1, V2 to the data ratewhich is possible as a result of the use of all common channels DSCHremains constant.

An additional degree of freedom is possible if not every data rate has afixed mapping, i.e. uniquely onto prescribed TFCI values, but insteadalternatives can be chosen. For the purposes of illustration, FIG. 8shows, for a connection V1, the incorporation of the configuration ofthe common channels DSCH into the information signaled by the TFCIvalues.

A TFCI value represents a particular configuration of the services S1 toS3. To date, only one TFCI value for each permitted combination wasappropriate. The extension by the configuration data for the commonchannels DSCH can now be used to allocate a particular servicecombination to different combinations of dedicated and common channelsDCH, DSCH. In FIG. 8, the TFCI values 2, 3 and 4 relate to the sameservice combination, but different allocated common channels DSCH aresignaled.

If this table is allocated to a number of connections V1, V2, variouscommon channels DSCH can be chosen as alternatives by selecting asuitable TFCI value 2, 3 or 4, in order to permit a high data rate forup to three connections V simultaneously. By contrast, the low totaldata rate in the second row can always be transmitted in the permanentlyallocated dedicated channel DCH. For this reason, no common channel DSCHis necessary.

The in-band signaling of the TFCI values is effected as shown in FIG. 9.Within frame-by-frame transmission of data together with otherinformation, capacity is also provided for transmitting the currentlychosen combination of the transport formats TF and allocation of thecommon channels DSCH in the form of the TFCI values. In the FDD mode ofUMTS, a frame lasts 10 ms, with bits of a pilot sequence serving forchannel estimation, bits being required for transmission powerregulation and bits being reserved for in-band signaling of the TFCI.Next comes a data component with user information. Error protectioncoding of the TFCI on, by way of example, 32 bits and scrambling of theuser information over a number of frames are not shown in FIG. 9.

Although the present invention has been described with reference tospecific embodiments, those of skill in the art will recognize thatchanges may be made thereto without departing from the spirit and scopeof the invention as set forth in the hereafter appended claims.

1. A method for transmitting data over a radio interface between a basestation and a plurality of subscriber stations in a radio communicationsystem, the method comprising the steps of: distinguishing channels in abroadband frequency band using individual spread codes, wherein at leastone common channel is allocated to a plurality of connections existingin parallel for use at successive times; signaling in-band asubsequently valid allocation of the at least one common channel for oneof the plurality of connections in at least one of the channels of thedata transmission using a respective TFCI value that specifies (1)combinations of data for a plurality of services to be transmittedwithin the at least one of the channels, (2) a data rate and (3) atleast one of the individual spread codes contained in the data rateallocated to the connection; agreeing upon a relationship among (1) theTFCI value and the combinations of data for a plurality of services tobe transmitted within the at least one of the channels, (2) the datarate, (3) the at least one of the individual spread codes contained inthe allocated data rate and (4) the at least one common channel to beused in a separate signaling channel; and transmitting the data in theat least one of the channels for data transmission based on theallocation.
 2. A method for transmitting data over a radio interfacebetween a base station and a plurality of subscriber stations in a radiocommunication system as claimed in claim 1, wherein the transmission ofdata occurs in a downlink direction from the base station to theplurality of subscriber stations.
 3. A method for transmitting data overa radio interface between a base station and a plurality of subscriberstations in a radio communication system as claimed in claim 2, whereina largest possible number of channels are allocated as the commonchannels, with at least one channel per connection being allocatedexclusively.
 4. A method for transmitting data over a radio interfacebetween a base station and a plurality of subscriber stations in a radiocommunication system as claimed in claim 3, wherein the common channelsare allocated for connections having a high maximum data rate.
 5. Amethod for transmitting data over a radio interface between a basestation and a plurality of subscriber stations in a radio communicationsystem as claimed in claim 3, wherein the common channels are allocatedfor connections having high data rate dynamics.
 6. A method fortransmitting data over a radio interface between a base station and aplurality of subscriber stations in a radio communication system asclaimed in claim 1, wherein, for a subset of the data rates, the in-bandsignaling can be used to select from a plurality of combinations ofchannels for a connection.
 7. A method for transmitting data over aradio interface between a base station and a plurality of subscriberstations in a radio communication system as claimed in claim 1, whereina relationship between the allocated data rate and the common channelsto be used is agreed upon at connection setup.
 8. A method fortransmitting data over a radio interface between a base station and aplurality of subscriber stations in a radio communication system asclaimed in claim 1, wherein a partial information item is used to signalin-band the individual data rates for the services within a connectionand the use of one or more channels.
 9. A radio communication system fortransmitting data over a radio interface between a base station and aplurality of subscriber stations, comprising: a plurality of channelsforming the radio interface in a broadband frequency band, the pluralityof channels being distinguished using individual spread codes, and atleast one common channel being allocated to a plurality of connectionsexisting in parallel for use at successive times; a transmitter fortransmitting a combination of data for a plurality of services on aconnection within at least one channel for data transmission between thebase station and the plurality of subscriber stations; and a signalingdevice for determining and signaling a subsequently valid allocation ofthe common channel for a connection using a respective TFCI value thatspecifies (1) combinations of data for a plurality of services to betransmitted within the at least one of the channels, (2) a data rate and(3) at least one of the individual spread codes, contained in the datarate, which is allocated to the connection, via in-band signaling in atleast one channel of the data transmission, wherein a relationship among(1) the TFCI values that specify combinations of data for a plurality ofservices to be transmitted within the at least one of the channels, (2)the data rate and (3) the at least one of the individual spread codescontained in the allocated data rate, and wherein the allocated commonchannel is transmitted in a separate signaling channel.
 10. A method fortransmitting data over a radio interface between a base station and aplurality of subscriber stations in a radio communication system, themethod comprising the steps of: identifying individual spread codes in aplurality of channels on a broadband frequency band; distinguishing saidchannels in accordance with said identified spread codes, wherein atleast one common channel is allocated to a plurality of connectionsexisting in parallel for use at successive times; signaling in-band anallocation of the at least one common channel for one of the pluralityof connections in at least one of the channels of the data transmissionusing a respective TFCI value that specifies (1) combinations of datafor a plurality of services to be transmitted within the at least one ofthe channels, (2) a data rate and (3) at least one of the individualspread codes contained in the data rate allocated to the connection;agreeing upon a relationship among (1) the TFCI value and thecombinations of data for a plurality of services to be transmittedwithin the at least one of the channels, (2) the data rate, (3) the atleast one of the individual spread codes contained in the allocated datarate, wherein the at least one common channel to be used is set in aseparate signaling channel; and transmitting the data in the at leastone of the channels for data transmission based on the allocation.